1. Field of the Invention
The present invention relates to a motor control method and apparatus, and more particularly to a control method and apparatus capable of improving a motor speed control signal so as to reduce noise and increase the operating efficiency while the motor is operating.
2. Description of the Related Art
Today, motor control methods are sophisticated and advanced, utilizing circuits to control motor rotation. Furthermore, circuits are used to change or limit motor rotational speed, along with other functions of motor control.
A well-known motor control apparatus is shown in FIG. 1. The motor control apparatus 1 includes the motor driver 10, the hall sensor 12, the coil switching circuit 14, and the pulse width modulator 16. The hall sensor 12 detects a phase signal generated while the motor is operating, and the phase signal is equal to the phase switched by coil set 20 of the motor. The motor driver 10 is electrically coupled to the hall sensor 12, receives the phase signal from hall sensor 12 to generate a motor speed control signal. The motor speed control signal usually consists of regular and continuous rectangular waves. FIG. 2 shows the waveform of the motor speed control signal 21. Ordinate A designates the amplitude of waveform, which can be represented as a voltage, while abscissa t designates time. The motor driver 10 is usually an application specific integrated circuit (ASIC), which is well known by those skilled in the art and easily acquired as an industrial product. Meanwhile, the coil switching circuit 14 often consists of two MOS switches. When the motor control signal 21 generated by the motor driver 10 is input into the coil switching circuit 14, the coil switching circuit 14 will output a motor speed control signal 21 sequentially into the coil set 20 of the motor so as to switch the current flow of two adjacent phases to sustain motor operation. Moreover, a pulse width modulator 16 can modulate motor speed control signal 21 as uniform-distributed rectangular waves by way of pulse width modulation (PWM). Referring to FIG. 3, after the motor speed control signal 21 is divided into several small rectangular waves, the motor control signal 21 is equalized to smaller amplitude according to the equivalent principle. Inputting the equivalent motor control signal 21 into the coil set 20 will slow down the rotational speed of the motor. However, when the coil set 20 is under the switching phases (for example, point P in FIG. 2), the current flow passing through the coil will be instantly switched to the opposite direction, and thus result in large noises during motor operation. Especially for a fan motor, large noises limit the application of the fan motor.